In the past few years, I’ve become fascinated with “good guy” bacteria — the bugs that live on and inside us, and keep us safe from disease and infection. It’s kind of awesome that we’re home to zillions of microbes. You’re a walking Starship Enterprise and the crew is doing maintenance and defense work on you even as we speak!

(Let me pause and say that if that concept make you a little squeamish, you may find the rest of this blog post grody).

Along these lines, I was fascinated to read of a recent study which concluded that gut bacteria may be the reason that babies born by c-section are twice as likely to be overweight later in childhood, compared with babies born vaginally. The study, in the Archives of Disease in Childhood, found a large disparity in childhood obesity rates between kids born by c-sec and those born vaginally, even after considering other factors such as mother’s weight, baby’s size and the length of time they were breastfed.

We already knew that babies born by c-section have an increased risk of post-birth infection vs. babies born vaginally, in part because of good-guy bacteria: as babies travel through the birth canal, and all the good bacteria that live there (yes, your vagina is filled with bacteria! It protects you from illness) coat the baby’s skin, providing your baby with an initial coating of anti-germ protection even as he’s being born. (A baby born by c-section on the other hand, comes out of the sterile amniotic sac, directly into a germ-filled operating room. Germs that cause illness have the opportunity to colonize his skin before mom’s good anti-sick bacteria can colonize and protect him. This is why skin-to-skin contact is especially important for babies born surgically — frequent contact helps the baby get a nice coating of protective bacteria from the “Mother Ship.”)

So, but here’s how this plays out with the obesity thing. Apparently the presence or absence of different gut bacteria play a role in how we use energy, respond to insulin and lay down fat. And babies born by c-section have different gut bacteria than those born vaginally, even years later. Why?

Take a step back. There’s bacteria in your gut, right? What happens to it? Mostly it lives inside you. Also, some of it comes out when you poop. So, you can find traces of it around your bottom. Pan the camera back and let’s think for a minute about how babies born vaginally could come into contact with their mom’s gut bacteria? As a another childbirth educator once quipped, “it’s not by accident that babies are born with their face an inch from your asshole.” They’re designed, apparently, to meet that part of you first so they can get exposed to your gut bacteria and, yes, ingest some (microscopic) amount, so it can colonize their gut. And that is apparently going to help them for the rest of their lives. Next step for the newborn is to be placed on mom’s belly, where he can get colonized with her external, protective skin bacteria, and after that onto mom’s breast where the colostrum in her breasts is filled with immune factors so that with the first swallow her body tells him: “all the stuff you were just exposed to is harmless for you, so don’t use your energy mount an immune response to any of it; you can use your energy to grow, stabilize temperature and sugar, and get acclimated, not for defense.” Her breastmilk also contains pro- and pre-biotics to further colonize his gut and protect him from the inside.

I think this is kind of awesome. Not the image of a baby with her nose in your rear end — sure, that’s kind of eww-y when you stop and think. But what’s totally magnificent to me is the way our bodies are designed to do this right. There are so many small things, invisible until we study them, which turn out to have tremendous lasting significance.

What can you do?

Don’t feel bad if you had a c-section, that kind of backward-focus doesn’t help. If you had a c-section, focus on behaviors that lean against any increased potential for obesity; we should all do that anyway. C-section can be a very, very important surgery, and when it’s medically necessary, it is a tool we are very lucky to be able to use, and to have such phenomenally good results from most of the time.

But what we all can do, I think, is maintain a kind of reverence for the body, and remember that no matter how sophistocated we are, and how good our technology, how advanced our medications, and how grateful we are for the way they save lives, nothing we can invent compares to the complicated beauty and grace of a functioning human body.

There is much we do not understand. When it comes to a body that is healthy, we should be very reserved about elective surgeries. And we ought to manage labors to minimize the likelihood of c-section, not just for all the reasons we know, but, even more, for the reasons we don’t know yet.

UPDATE, 7/13/12: Here’s a great article exploring the science of this issue, from Science and Sensibility.